1. Field of the Invention
The present invention relates to a flame retarding resin composition having good mechanical properties and good moldability. More particularly, the invention relates to a resin composition having high flame retardance, high impact strength and good moldability comprising: (1) one or more ternary resins selected from the group consisting of an acrylonitrile-butadiene-styrene ternary resin (hereafter called "ABS resin"); an acrylonitrile-acrylic rubber-styrene ternary resin (hereafter called "AAS resin"); an acrylonitrile/ethylene-propylene rubber/styrene ternary resin (hereafter called "AES resin"); and an acrylonitrile/ethylene-vinyl acetate copolymer/styrene ternary resin (hereafter called "AEvS resin"); (2) an acrylonitrile-chlorinated polyethylene-styrene ternary resin (hereafter called "ACS resin"); and (3) antimony trioxide.
2. Description of the Prior Art
ABS resin, AAS resin, AES resin and AEvS resin are known as engineering plastic structural materials having high mechanical properties, in particular, excellent tensile strength and impact strength. However, they have the fault of combustibility. Since regulations regarding the acceptable degree of flame retardance have recently come into force or have been strengthed for products in the fields of materials for buildings, vehicles, electronic and electric appliances in which these resins are used, there has been an urgent need for flame retardant resins of the above-mentioned ternary types, and various methods to increase the flame retardance of such ternary resins have been proposed or attempted.
For example, for rendering ABS resin flame retardant various flame retarding agents have been proposed. That is, it is known that ABS resin can be rendered flame retardant by incorporating therein an organic flame retarding agent such as an organohalogen compound, a halogenated phosphate ester, or a phosphate, or a mixture of an organic flame retarding agent and an auxiliary inorganic flame retarding agent, such as antimony trioxide, which further increases the flame retardant effect. However, for high flame retardancy a large amount of flame retarding agent is required, and although the purpose of rendering the ABS resin flame retardant may be attained by the addition of such a flame retarding agent, the addition of the flame retarding agent to ABS resin, etc., is accompanied by the undesirable effect that the excellent impact strength and tensile strength, as well as other preferred properties, of the resins are greatly reduced, and at the same time dripping during combustion occurs. For example, when general and inexpensive chlorinated paraffins are employed as a flame retarding agent for these resins, the impact strength of the resins is greatly reduced.
As described in the specification of, e.g., Japanese Patent Publication No. 2791/'58, a method has been proposed wherein ABS resin is rendered flame retardant by blending the ABS resin with polyvinyl chloride. This method has some merits in that the resin maintains proper hardness and toughness and also the reduction in impact strength is comparatively low due to the properties of polyvinyl chloride. On the other hand, because the thermal decomposition temperature of polyvinyl chloride is low, the molding temperature or working temperature for such a resin composition containing polyvinyl chloride must be lower than that for ABS resin per se to prevent thermal decomposition of polyvinyl chloride at molding or working, i.e., the molding temperature of the resin composition is lower than 180.degree.C. Furthermore, the addition of polyvinyl chloride reduces the fluidity of the resin, and hence tends to greatly reduce the molding or working property of the resin. Moreover, the addition of a large amount of polyvinyl chloride having a low heat distortion temperature is undesirable for engineering plastics in which the heat distortion temperature is an important factor.
As described in the specification of U.S. Pat. No. 3,494,982, a further method comprises rendering ABS resin flame retardant by blending chlorinated polyethylene therewith. This method enables a high molding or working temperature to be used with the blend resin (as compared with the case of blending polyvinyl chloride) but the fluidity and the heat distortion temperature of the resin are reduced.
As mentioned above, conventional methods of rendering resins flame retardant may have the merit of rendering the resin flame retardant but conventional methods invariably result in a reduction in the thermal properties, impact strength, tensile strength and the molding and working properties of the resin. In other words, the resins thus rendered flame retardant do not have desirable properties as resins for molding.
Further, flame retarding agents are generally expensive, commercially availability is unstable, and the addition of a large amount of such flame retarding agents causes undersirable effects in resin properties and increases the cost of products made from the resins.